Understanding the Evolution of Global Atmospheric Rivers with Vapor Kinetic Energy Framework

TL;DR

The paper develops a global Vapor Kinetic Energy (VKE) budget framework to understand atmospheric rivers (ARs) across basins, introducing two formulations, $IKEV$ and $IVTE$. It shows that AR growth is mainly controlled by the conversion of potential energy to kinetic energy ($PE\rightarrow KE$), AR decay is dominated by condensation and turbulence, and AR propagation is governed by downstream convergence of vapor-kinetic-energy flux. Regional variation is tied to baroclinic instability and topography, with stronger PE-to-KE conversion in moister, more unstable regions and near coastal mountains where dissipation frequently offsets growth. The VKE framework provides a powerful diagnostic for how physical processes shape AR evolution and regional variability, with implications for understanding AR behavior in a changing climate.

Abstract

Atmospheric rivers (ARs) often cause damaging winds, rainfall, and floods. However, the physical mechanisms governing their evolution remain poorly understood. To close this gap, we perform a global Vapor Kinetic Energy (VKE) budget analysis. Using two formulations of VKE, we show that ARs are governed by similar mechanisms regardless of ocean basins. ARs intensify primarily through the conversion of potential energy to kinetic energy (PE-to-KE), with horizontal convergence of vapor kinetic energy providing a secondary contribution in some regions. ARs decay mainly through condensation and turbulent dissipation, while their propagation is governed by the downstream convergence and upstream divergence of vapor kinetic energy. We also find PE-to-KE conversion varies spatially and strengthens in regions of greater baroclinic instability or enhanced topographic lifting, e.g., along North America's west coast. Collectively, these findings demonstrate that the VKE framework provides a powerful diagnostic for how physical processes shape AR evolution and regional variability.

Figures (13)

• Figure 1: AR frequency with different variables in 2010-2019. Panel a shows the AR frequency with IVT. Panel b shows the AR frequency with IKEV. Panel c shows the AR frequency with IVTE. The tropical region between $\pm20^\circ$ latitude is not considered as AR in the detection. The black dashed lines are the representative locations of the five frequent-AR ocean basins.
• Figure 2: A Hovmöller diagram on the latitudinal-averaged (from 22.75$^\circ$N to 52.75$^\circ$N) AR composite in North Pacific. The black contours show the IKEV composite. The colored fields indicate the regressed vertically-integrated IKEV tendency variable. Panel (a) shows for IKEV tendency; panel (b) shows for horizontal convergence of the KEV flux; Panel (c) shows the PE conversion to KE; panel (d) shows the vertical convergence of the KEV flux; panel (e) shows the turbulence dissipation; panel (f) shows the condensation of vapor.
• Figure 3: The global IKEV budget analysis on the AR evolution. Panel (a) shows the contribution to the growth/decay. Panel (b) shows the contribution to the movement. Each vertical panel shows the contribution from the tendency terms in each basin. The horizontal arrows indicate the center of each composite. The red is for the PE conversion to KE. The orange is for the horizontal convergence of the KEV flux. The green is for the vertical convergence of KEV flux. The purple is for the dissipation from turbulence and condensation. The blue is for the net IKEV tendency.
• Figure 4: The composites of IKEV tendencies in the northeast Pacific. In all panels, the green arrows are the $850$ hPa wind profile and the grey shadings are the height of the topography. The brown contours are the IKEV composites (The levels are at 30%, 50%, 70%, and 90% of the maximum IKEV values). The colored fields correspond to different composites. Panel (a) shows the vertically-integrated PE-to-KE conversion. Panel (b) shows the vertically-integrated MWBC. Panel (c) shows the vertically-integrated moisture-weighted convergence of geopotential. Panel (d) shows the vertically-integrated condensation of vapor. Panel (e) shows the vertically-integrated turbulence dissipation. Note that these tendencies are moisture-weighted, and the color ranges of each panel are different.
• Figure S1: The standard deviation of IKEV before (left) and after (right) removing tropical cyclones (TC). Before the removal, there is strong IKEV in the southwest Pacific and Atlantic in JJA and SON. After explicitly removing TC, the regions of high IKEV standard deviation are in elongated shapes, similar to that of the AR frequency map in figure 1.